940 



THE VOYAGE OF H.M.S. CHALLENGES. 



I. Subfamily 



Lithocircida. 



No typical basal feet on 

 the base of the ring (no 

 cortinar feet). 



II. Subfamily 



Cortinida. 



Three or four typical basal 

 feet on the ring (cortinar 

 feet). 



Synopsis of the Genera of Stephanida. 



{Ring smooth or thorny, with- 

 out branched spines. 

 Ring armed with branched 



( 



spines, 



I" Ring smooth or thorny, with- 



Ring dipleuric, bilateral ; j out branched spines, 

 dorsal and ventral bow -j 

 different Ring armed with branched 



[ spines. 



Three basal feet (and an ( 

 apical horn). | 



One caudal and two lateral 

 feet, 



Four basal feet (and an / Two sagittal and two lateral 

 apical horn). ( feet, 



401. 



402. 



403. 



404. 



405. 



406. 



Arcliicircus. 



Lithocircus. 



Zygocircus. 



Dendrocircus. 



Cortina. 



Stephanium. 



Subfamily 1. LITHOCIRCIDA, Haeckel. 

 Definition. S tephanida without typical basal feet or cortinar feet. 



Genus 401. Archicircus, 1 n. gen. 



Definition. S tephanida with a simple amphithect or diphragmatic ring, smooth 

 or thorny, without branched spines and basal feet. 



The genus Archicircus is the most primitive and simplest form of all Stephoidea, 

 and probably the common ancestral form, not only of this suborder, but of the greater 

 number of all NASSELLARIA (compare above, p. 893). The skeleton consists only of a 

 quite simple sagittal ring, in which commonly a slight difference of both poles of the 

 main axis (basal and apical pole) is visible, but no difference between the dorsal and the 

 ventral bow of the ring. In my Prodromus (1881, p. 447) the species of Archicircus 

 were disposed partly in the subgenus Monostephus, partly in the genus Lithocircus. 



Subgenus 1. Monostephus, Haeckel, 1881, Prodromus, p. 447. 

 Definition. Ring circular, elliptical, or ovate, without prominent corners. 



1 . Archicircus princeps, n. sp. 



Gate circular. King circular, smooth, its transverse section also circular. The simplest form of 

 all Stephoidea. 



Dimensions. Diameter of the gate 0'05 to - 08 ; thickness of the ring O'OOG to O'OOS. 

 Habitat. Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms. 



1 Archicircus = Primordial ring; ajjc'i *'j*of. 



